function Q = observe_plucker( T,X,P)
%function Q = observe_plucker( T,X,P)

Q = [];
for i=1:size(T,2);
   for j=1:size(X,2);
      c = P{j}(:,4);
      t = T{i}*X{j};
      q = t(1:3)-c;
      q = q/norm( q );
      qp = cross( q,c);
      Q=[Q [j;i;q;qp]];
   end
end